The present invention relates to a high-voltage generating transformer and particularly to a high-voltage generating transformer for use in a discharge lamp lighting circuit for a headlight of a vehicle.
A conventional high-voltage generating transformer of the type that a primary coil-wound bobbin and a secondary coil-wound bobbin are assembled coaxially relative to a center core has a large size because of providing a large transformer ratio (i.e., the ratio of the number of turns in the secondary winding to the number of the primary winding) to produce a high voltage at the secondary side of the transformer.
A typical attempt has been made to reduce in size and weight a conventional transformer by reducing the number of turns in its primary coil to 3-5 turns and correspondingly reducing the number of turns in the secondary coil. However, the attempt resulted in that the working efficiency of the transformer was decreased by an increased leakage of magnetic flux resulted from the decreased coverage ratio of the primary coil to the secondary coil.
As described above, the conventional high-voltage generating transformer having coaxially mounted primary and secondary coil-wound bobbins with a center core may be reduced in size and weight by considerably reducing the number of turns in the primary winding to 3-5 but encounters a problem of increasing leakage of magnetic flux and decreasing the working efficiency. This makes the transformer be unable to generate a sufficiently high secondary voltage.
Accordingly, an object of the present invention is to provide a high-voltage generating transformer having coaxially mounted primary and secondary coil-wound bobbins with a center core, which is reduced in size and weight by minimizing the number of turns in the primary winding and, at the same time, can obtain a sufficiently high voltage at its secondary side, effectively preventing leakage of magnetic flux. This is realized by spirally winding an element wire around the primary coil bobbin in forward and backward direction to form thereon the primary coil whose axial length is long enough to meet with the secondary coil and whose starting and terminating ends are disposed at the same side of the bobbin.